Out of all the cans I've heard I've settled on the DT531 as the best headphone for hip-hop & rap. First of all the comfort is better than the DT770 and K240S; the silver velour earpads and light headband means a nearly invisible fit. While the DT770 has more bass, it can simply be overpowering and distracting (even for the bassiest rap) and the mids sound recessed while the treble is a bit too harsh for me (its headband also cause me some grief after a couple hours). The K240S is less comfortable than the DT531 due to its pleather pads and slightly annoying headband. The K240S has arguable equal bass (I prefer the DT531's more controlled bass but some may prefer the K240's more powerful bass). I can't use the DT770 for anything because of its extremely unbalanced sound - there is plenty of hip-hop that benefits from the detail and sweet midrange that the DT531 and K240S provide. Considering the absence of the DT531 in the US (I had to buy it used for more than retail) the K240S is a very appropriate replacement (some may even prefer its sound). The DT770 may "wow" you initially with the sheer volume of bass, but the DT531 and K240S are much easier to live with in the long run and groove even better - the groove is the most important aspect of hip hop, IMO. Some hip-hop albums I've been enjoying with my DT531:
The Low End Theory (A Tribe Called Quest)
Like Water for Chocolate (Common)
The Platform (Dilated Peoples)
The Chronic (Dr. Dre)
Haiku d'Etat (Haiku d'Etat)
Full Circle (Hieroglyphics)
AmeriKKKa's Most Wanted (Ice Cube)
Straight Outta Compton (N.W.A)
Ozomatli (Ozomatli)
Doggystyle (Snoop Doggy Dogg)
There area many moments on these and other albums that benefit not only from great groovalizer bass, but also from clear midrange and extended treble. One would be very happy with the K240S and DT531.